Rheostat control system



Nov. 15, 1955 A. P. CHARBONNEAU RHEOSTAT CONTROL SYSTEM Eiled Sept. 30,1954 ACC. OFF DB RHEOSTAT TAP POSITION RHEOSTAT TAP POSITON UnitedStates Patent RHEOSTAT CONTROL SYSTEM Allan P. Charbonneau, Wauwatosa,Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation ofDelaware This invention relates to a rheostat control system.

While not limited thereto the present invention is particularly adaptedfor controlling the excitation of the fields of exciters which supplythe fields of main generators in locomotive diesel-electric drives.

It is a primary object of the present invention to provide an improvedrheostat control system affording either series or combined series andpotentiometer type rheostat control selectively.

Another more specific object, through use of such rheostat control inconjunction with locomotive diesel-electric drives, is to provide onepattern of exciter field excitation vs. rheostat position foraccelerating and running operation and another for dynamic brakingoperation, and

A still further specific object is to obtain simplification of controlfor locomotive diesel-electric drives through employment of theaforementioned rheostat control.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustrate a preferred embodiment of theinvention which will now be described in detail, it being understoodthat the embodiment illustrated is susceptible of modification inrespect of details without departing from the scope of the appendedclaims.

In the drawings:

Figure l is a diagrammatic showing of a rheostat control systemincorporating the invention as applied to the control of an exciterfield in a diesel-electric drive.

Fig. 2 is a graph depicting the variations in field current and rheostatresistance with change in tap position for one operating condition ofthe control system of Fig. 1, and

Fig. 3 is a graph depicting the variation in field current, totalcurrent and resistance of another rheostat with change in tap positionin another operating condition of the control system of Fig. 1.

Referring to Fig. 1, the reference numeral DE designates a diesel enginewhich drives a D. C. main generator G and an exciter E of a locomotivediesel-electric drive. Generator G has a field winding F which isconnected across terminals of armature a and exciter E. Exciter E has afield winding f which is connected at one end to the negative potentialline L2 of a source of D. C. voltage supply and at its other end to astationary contact S2 of a single pole double throw switch S and to thecontactor S1 of said switch in series with a current limiting fixedresistor r. Contactor S1 is connected to the adjustable tap 5 of arheostat 6 which also has a resistance element 7 connected at one end tothe positive potential line L1 of the aforementioned source.

Stationary contact S3 of switch S is connected to adjustable tap 8 of arheostat 9 which also has a resistance element 10 connected at one endto supply line L2. A rotatable shaft, schematically depicted at 11, isadapted to simultaneously rotate taps 5 and 8 of rheostats 6 and 9 tocorresponding points on their respective associated resistance elementsunder the direction of a load regulating governor schematically depictedat 15. Governor which is schematically depicted as being driven by thediesel engine DE may be assumed to be responsive to changes in speed andload on engine DE to rotate shaft 11 in accordance therewith.

A master throttle controller, which is schematically depicted at 16 andwhich may be of any preferred type, is shown as having mechanicalconnection with the contactor S1 of switch S. Controller 16, for thesake of simplifying the understanding of the present invention, isdepicted as having only three operating positions namely Off, Ace (foraccelerating) and DB (for dynamic braking). It may be assumed thatoperation of the controller 16 to Ace position will operate contactor S1to engage contact S2 as depicted in Fig. 1, and that operation ofcontroller 16 to either the Off or DB positions will operate contactorS1 to engage contact S3.

With controller 16 moved to Acc" position and contactor S1 closed tocontact S2, field winding 1 of exciter E will be connected betweensupply lines L1 and L2 in series with rheostat 6, and the energizationof such field winding may be assumed to vary with change in position oftap 5 on resistance element 7 according to the curve H of Fig. 2. Theamount of resistance of rheostat 6 effectively connected in series withfield winding 1 for the same changes in tap position may be assumed tovary according to the curve J. The form of curve I will of course dependupon the total amount of resistance of element 6 and its ohmic taper perunit of length and may be varied to meet particular conditions. Thevariation in exciter field current depicted by curve H has been found tobe particularly suitable when the main generator is supplying the truckdriving motors during acceleration and normal running.

When controller 16 is moved to DB position contactor S1 will then beclosed to contact S3 and the rheostat 9 will then be connected inparallel with the series combination of resistor r and field winding fof exciter E between contactor S1 and supply line L2. It will beobserved that under these operating conditions that for every change inseries resistance afforded by rheostat 6 that there will be a change inparallel branch resistance afforded by rheostat 9. Assuming that theeffective resistance afforded by resistance element 9 varies inaccordance with the straight line K of Fig. 3 for changes in position oftap 8, and that the change in resistance afforded by rheostat 6 is inaccordance with curve of Fig. 2 as aforeindicated, then the totalcurrent flowing in the circuit will vary as the curve L and the currentflowing through the exciter field f will vary according to the curve Mof Fig. 3. The variation in energization of the exciter field winding inaccordance with curve M which affords zero energization in one extremeposition of the rheostats taps is desirable when the truck drivingmotors of a locomotivediesel-electric drive are connected for dynamicbraking operation.

It will be apparent that the same results can be obtained in the systemof Fig. 1 if the electrical connections to the end terminals and tap ofrheostat 6 and/or rheostat 9 are interchanged. The arrangement ofwindings and taps of rheostats 6 and 9 can take various preferred forms.

I claim:

1. In combination, a source of voltage, a load device, control meanscomprising a first rheostat, a second rheostat and means operable tosimultaneously adjust the taps of said rheostats on their respectiveresistance elements, and means operable to selectively connect said loaddevice either in series with said first rheostat across said source ofvoltage or in parallel with said second rheostat and together with thelatter in series with said first rheostat across said voltage source.

2. The combination according to claim 1 characterized by said taps ofsaid rheostats being adjusted simultaneously to corresponding points ontheir respective resistance elements.

3. The combination according to claim 1 together with a resistorconnected in series with said load device by operation of the lastmentioned means to effect the last recited connections.

4. In a diesel-electric drive, the combination with an exciter having afield winding, :1 main generator having a field winding connected to thearmature of said exciter and a diesel engine driving said exciter andgenerator, of

a source of D. C. voltage, a first rheostat, a second rheostat, meansproviding simultaneous adjustment of the taps of said rheostats on theirrespective resistance elements in accordance with changes in speed andload on said engine, and means operable to selectively connect saidexciter field winding either in series with the first rheostat acrosssaid source of voltage or in parallel with the said second rheostat andtogether with the latter in series with said first rheostat across saidsource of voltage.

No references cited.

